Zong-Jun Li

Electrochemical and H/D-Labeling Study of Oxazolino[60]Fullerene Rearrangement

Isomerization of an oxazoline cycle from a [6,6]- to [5,6]-junction on the C(60) sphere of dianionic [60]fullero-oxazoline (1(2-)) during a 1,4-addition is studied by electrochemistry and a stepwise addition of PhCH(2)Br and PhCD(2)Br. Cyclic voltammerty of the in situ generated 1(2-) shows a very unusual positive shift for the anodic peak corresponding to the oxidation of 1(2-), indicating that the C(60) cage of dianionic 1 bears only one unit negative charge due to the heterolytic cleavage of the C(60)-O bond. Further study with a stepwise addition of PhCH(2)Br and PhCD(2)Br, which are used to differentiate the aryl groups added at each step onto dianionic 1, shows explicitly there is an exclusive selectivity of the C-O bond for the ring-opening and ring-closure during the isomerization of the heterocycle. A reaction mechanism is proposed on the basis of the experimental results and computational calculations.

Reactions of anionic oxygen nucleophiles with C60 revisited.

Reactions of C(60) with oxygen nucleophiles of HO(-) and CH(3)O(-) are revisited in PhCN in the presence of PhCH(2)Br. Different from previous results that such reactions lead to the formation of complex mixtures, well-structured C(60) oxazolines are obtained when HO(-) is involved, while di- and tetraadducts with methoxy and benzyl addends are obtained when CH(3)O(-) is engaged. The reactions are followed by in situ vis-near-IR spectroscopy, which reveals further information for the reactions.

Formation of singly bonded PhCH2C60-C60CH2Ph dimers from 1,2-(PhCH2)HC60 via electroreductive C60-H activation.

Singly bonded PhCH(2)C(60)-C(60)CH(2)Ph dimers are generated via controlled-potential bulk electroreduction and electrooxidation of 1,2-(PhCH(2))HC(60). The reaction mixture was purified by HPLC, and the isolated fraction was characterized with single-crystal X-ray diffractions, (1)H and (13)NMR, MS, elemental analysis, and cyclic voltammetry. It was shown that the fraction consists of two HPLC-inseparable PhCH(2)C(60)-C(60)CH(2)Ph regioisomers, which are assigned as the meso and racemic regioisomers. The bulk electrolysis processes for the formation of the dimers were followed by in situ cyclic voltammetry and were further corroborated with an in situ voltammetric titration of 1,2-(PhCH(2))HC(60) with tetra-n-butylammonium hydroxide (TBAOH), on the basis of which a reaction mechanism is proposed.

Reaction of C602- with Organic Halides Revisited in DMF: Proton Transfer from Water to RC60- and Unexpected Formation of 1,2-Dihydro[60]fullerenes

The reactions of dianionic C(60) with organic halides, which have been studied extensively in benzonitrile (PhCN), are revisited in a different solvent medium, N,N-dimethylformamide (DMF), by using ArCH(2)Br (Ar = Ph, C(6)H(4)CH(3), C(6)H(4)Br). Interestingly, instead of the 1,4-R(2)C(60) adducts, which are the typical products when the reactions are carried out in PhCN, the 1,2-dihydro[60]fullerenes (1,2-HRC(60)) have been obtained as the major products in DMF, except for the case of o-CH(3)C(6)H(4)CH(2)Br probably due to the steric effect. The obtained 1,2-dihydro[60]fullerenes have been characterized with single-crystal diffraction, (1)H and (13)C NMR, high-resolution mass spectrometry (HRMS), and UV-vis. Further examination with deuterated reagents including PhCD(2)Br, DMF-d(7), and D(2)O has revealed that the fullerenyl hydrogen of 1,2-dihydrofullerenes originates from traces of water residue in DMF. When the reaction is re-examined in PhCN with the addition of an excessive amount of water, the yield of 1,2-dihydrofullerene increases significantly, but is still lower compared with that obtained in DMF, demonstrating a considerable solvent effect on the reactivity of C(60)(2-). A possible mechanism accounting for such a difference is proposed. The work has presented an alternative protocol for effective preparation of 1,2-dihydro[60]fullerenes, and may also provide clues toward a better understanding of the proton transfer process for anionic C(60)-mediated reducing reactions involving H(2)O.

Regioselective Oxazolination of C702– and Formation of cis-1 C70 Adduct with Respect to the Apical Pentagon

Oxazolination of C(70) has been achieved via the aerobic oxidation of C(70)(2-) in the presence of PhCN. Only one C(70) oxazoline regioisomer (1) is obtained, indicating that the oxazolination of C(70)(2-) occurs with an unusual regioselectivity. Further benzylation of 1(2-) with benzyl bromide leads to the formation of the first cis-1 C(70) derivative with respect to the apical pentagon (2), as shown by the X-ray single-crystal structure and various spectral characterizations. The structure of the obtained C(70) oxazoline (1) is resolved with H/D labeling benzylation and HMBC (heteronuclear multiple bond coherence) NMR on the basis of the structure of 2. The result shows that for compound 1, the O atom is selectively bonded to the C1, while the N atom is bonded to the C2 of C(70). The exhibited regioselectivity for the orientation of oxazolino group on C(70) is further rationalized with computational calculations, and a reaction mechanism for the oxazolination of C(70)(2-) is proposed.

Reductive Benzylation of C60 Imidazoline with a Bulky Addend

Reductive benzylation of C60 imidazoline with a bulky addend affords two 1,2,3,16-adducts (2 and 4) and one 1,2,3,4-adduct (3). Experimental and computational results indicate that the sterically favored 2 is more stable than the electronically favored 3. However, an opposite stability order is shown for the dianions of 2 and 3.

Hydroxide-initiated conversion of aromatic nitriles to imidazolines: fullerenes vs TCNE.

Transformation of aromatic nitriles to imidazolines has been achieved under basic conditions with the electron-deficient C60 and C70 fullerenes, but not with the electron-deficient olefin of tetracyanoethylene (TCNE). In situ UV-vis-NIR indicates that the ability of RC60(-) to undergo single-electron transfer (SET) to C60 is crucial for the reaction.

Oxygen-Bridged 1,2-1′,4′-RC60–O–RC60 Unsymmetrical Dimer

A novel oxygen-bridged unsymmetrical dimer composed of C60 cages with 1,2- and 1,4-configurations is obtained. The dimer is interesting due to the existence of only one regioisomer, unique regioselectivity, presence of organo functionalities, and exhibition of stepwise reductions via the alternative sequential electron transfer to the 1,4- and 1,2-C60 cages.

Oxazolination of 1,4-(PhCH2)2C60: toward a better understanding of multiadditions of heteroaddends.

Multiadditions of heteroaddends to C(60) are achieved via the oxazolination reaction of 1,4-(PhCH(2))(2)C(60) with OH(-) and PhCN, which exhibit a unique regioselectivity regarding the addition sites of the heteroatoms.

A room-temperature fluorescence study of organofullerenes: cis-1 bisadduct with unusual blue-shifted emissions.

C(60) derivatives have shown enhanced fluorescent emissions with respect to C(60) due to the lowering of molecular symmetry and have demonstrated promising potentials as novel organoelectronic materials for application in light-emitting diodes. Previous work has indicated that the fluorescent properties of functionalized C(60) are mainly affected by the addition patterns, rather than the nature of addends. However, no report on the fluorescence of C(60)cis-1 bisadducts, one of the most favorable types of C(60) bisadducts, has appeared up to date. Herein, the fluorescent properties of two structurally related C(60)cis-1 bisadducts of fullerooxazolines, 1 and 2, are examined at room temperature. It shows that a significant difference exists for the fluorescent spectra of 1 and 2, where 1 displays a rather strong unusual blue-shifted emission band, even though the two compounds have the same addition pattern. Monoadducts bearing individual addends of 1 and 2, along with 1a and 1b, which have one PhCD(2)- positioned either next to the C(60)-N or C(60)-O bond, are also examined in order to gain a better understanding of such difference. The results indicate that the unusual blue-shifted emissions for 1 are likely to originate from the vibrational interactions of the addends, suggesting that the fluorescent emissions of C(60) derivatives can be tuned not only by the addition patterns, but also by the nature of the adducts. Density functional theory and time-dependent density functional theory calculations are performed to rationalize the experimental observations.